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This newsletter is e-mailed by McCrometer monthly to subscribers worldwide. It consists of flow measurement information of interest for professionals in this field.

For More information on our complete line of flowmeters go to: <<http://www.mccrometer.com>>

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McCrometer: Newsletter for October 2002

Choosing the Optimum Flow Measurement System for Cryogenic Applications

Liquefied gases will experience "strong demand growth in the coming years", says Jon Chadwick, Director of Shell Gas & Power. This spells increased demand for ways to transport and meter these types of gases. Here we look at the some of the difficulties in measuring liquefied gas flow.

Liquefied gases are generally clean liquids, but usually very cold (e.g. nitrogen's boiling point is -196 deg C (-321 deg F). Not only must the physical properties of the fluid be known at the position of flow measurement, but it is also essential the liquid remains in that phase during the measurement process and is not converted to the gas phase. Plus, these liquids generally have poor lubricity and care must be exercised if the flowmeter has moving parts.

What can be done to overcome these difficulties? It is relatively easy to select materials that will not become brittle and fail at low temperatures, although you still need to know how the metal behaves at these very low temperatures. In addition, if elastomers were being used, care must be made in their selection; for example, it is not possible to use a conventional ball prover for liquefied gases, so piston provers are necessary. Associated instrumentation must also be carefully selected to avoid failure. The company producing the fluid should know its physical properties, often not found in standard textbooks or International Standards, as the flow measurement technologist has to rely on their expertise.

Liquid flow meters can generally be used for liquefied gas measurement but one must choose carefully. Liquid turbine meters have been used successfully for a number of years. However, because of pressure drop through the meter and rotating element, it is necessary to maintain a back pressure onto the turbine to avoid any vapor breakout.

Coriolis meters have also been used in some of these applications but are limited in size. DP meters can be successful provided you are careful in selecting the DP and pressure transmitters. The V-Cone has a number of benefits here: it does not have any moving parts; it can be made in materials suitable for the liquid; it does not require long upstream and downstream piping; and it does not require in-situ calibration. They have been used in many liquefied gas applications, including a NASA application for liquefied argon, hydrogen and helium.

For more information on McCrometer's line of flowmeters for liquefied gas applications, contact McCrometer at 951-652-6811 or visit our web-site at www.mccrometer.com <http://www.mccrometer.com>.
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Copyright 2002 McCrometer